This invention relates to washing- or cleaning-active shapes, above all tablets, such as detergent tablets, dishwasher tablets, stain remover tablets or water softening tablets, for use in the home, more particularly for use in machines, to a process for the production of these shapes and to their use.
Washing- or cleaning-active shapes, more particularly tablets, have a number of advantages over powder-form compositions, including easy handling, simple dosing and low packaging volumes. However, problems arise out of the fact that comparatively high pressures have to be applied in the compression of the powder-form constituents in order to achieve adequate dimensional stability and fracture resistance. On account of the high compression involved, tablets of the type in question often show unsatisfactory disintegrating and dissolving properties in use so that the active substances are reduced too slowly in the washing or cleaning cycle and textiles in particular are in danger of being left with residues after the wash cycle.
The problem of the slow disintegration of tablets has been known for some time, more especially in the pharmaceutical industry. Here, the problem has been overcome or at least eased by the addition of certain disintegration aids known as tablet disintegrators. According to Römpp (9th Edition, Vol. 6, page 4440) and Voigt “Lehrbuch der pharmazeutischen Technologie” (6th Edition, 1987), tablet disintegrators are auxiliaries which provide for the rapid disintegration of tablets in water or gastric juices and for the release of the pharmaceuticals in an absorbable form. According to their action mechanism, they are classed as substances which increase the porosity or capillarity (“wick effect”) of tablets and which have a high adsorption capacity for water, as gas-evolving substances for effervescent tablets or as hydrophilicizing agents which ensure that the constituent particles of tablets are wetted in water. The first class includes the substances known as traditional disintegrating agents, such as starch, cellulose and cellulose derivatives, alginates, dextrans, crosslinked polyvinyl pyrrolidones and many others while the second class includes systems of weak acids and carbonate-containing agents, more particularly citric acid and tartaric acid in combination with hydrogen carbonate or carbonate. Examples of the third class are polyethylene glycol sorbitan fatty acid esters.
Thus, it is proposed in German patent application 938 566 to convert acetyl salicylic acid before compression into granules and, after complete but careful drying, to coat the granules thus formed with highly disperse silica. The acetyl salicylic acid granules coated with the highly disperse silica powder may then be mixed with other tablet ingredients, which may be present in powder form or granular form, and the resulting mixture is tabletted. The separating layer of highly disperse silica not only acts as an insulating layer and as protection against unwanted reactions, it also contributes towards the rapid disintegration of the tablets, even after prolonged storage.
German patent application 12 28 029 describes a process for the production of tablets in which powder mixtures—without preliminary granulation—are first mixed with cellulose powder and optionally highly disperse silica and the resulting mixture is compressed, in one preferred embodiment after grinding.
According to German patent application 41 21 127, a particularly effective auxiliary in the production of pharmaceutical tablets contains cellulose particles with a coating material fixed to their surface. The auxiliary is used in the form of fine particles, mean particle sizes below 200 μm being described as particularly advantageous. These fine-particle auxiliaries, which—in the production of pharmaceuticals—lead to tablets with both a relatively high fracture resistance and a relatively high disintegration rate, are produced in particular by a grinding process carried out in a ball mill.
Accordingly, conventional tablet disintegration belonging to the first class mentioned above are normally either mixed in very fine-particle form with the other tablet ingredients, which may be present in the form of fine particles or granules, before compression or the other tablet ingredients are coated or powdered/dusted with the tablet disintegrator.
According to the teaching of European patent EP-B 0 523 099, disintegrators known from the production of pharmaceuticals may also be used in detergents or cleaning products. The disintegrators mentioned include swellable layer silicates, such as bentonites, natural materials and derivatives thereof based on starch and cellulose, alginates and the like, potato starch, methyl cellulose and/or hydroxypropyl cellulose. These disintegrators may be mixed with, or even incorporated in, the granules to be compressed.
According to International patent application WO-A-96/06156 also, it can be of advantage to incorporate disintegrators in detergent or dishwasher tablets. Once again, microcrystalline cellulose, sugars, such as sorbitol, and also layer silicates, more particularly fine-particle swellable layer silicates of the bentonite and smectite type, are mentioned as typical disintegrators. Substances which contribute towards gas formation, such as citric acid, bisulfate, bicarbonate, carbonate and percarbonate, are also mentioned as possible disintegration aids.
Although neither of the last two prior-art documents cited above specifies the exact particle size distribution which suitable disintegrators are supposed to have, figures relating to the microcrystallinity of the cellulose and the particle fineness of the layer silicates suggest to the expert, above all in connection with the literature known from the production of pharmaceutical tablets, that conventional disintegrators are supposed to be used in fine-particle form. This is consistent with the fact that, hitherto, relatively coarse products obtained, for example, by granulation of fine powders, which are expressly marketed as tablet disintegrators, have not been commercially available.
European patent applications EP-A0 466 485, EP-A-0 522 766, EP-A-0 711 827, EP-A-0 711 828 and EP-A-0 716 144 describe the production of cleaning-active tablets in which compacted particulate material with a particle size of 180 to 2000 μm is used. The resulting tablets may have both a homogeneous structure and a heterogeneous structure. According to EP-A-0 522 766, the surfactant- and builder-containing particles at least are coated with a solution or dispersion of a binder/disintegration aid, more particularly polyethylene glycol. Other binders/disintegration aids are the already repeatedly described and known disintegrating agents, for example starches and starch derivatives, commercially available cellulose derivatives, such as crosslinked and modified cellulose, microcrystalline cellulose fibers, crosslinked polyvinyl pyrrolidones, layer silicates, etc. Other suitable coating materials are weak acids, such as citric acid or tartaric acid which, in conjunction with carbonate-containing sources, lead to effervescent effects on contact with water and which, according to Römpp's definition, belong to the second class of disintegrating agents. In these cases, too, no specific details are provided as to the particle size distribution of the disintegrators. However, they are all applied to the surface of granules. This is done either—as mentioned—in liquid to disperse form or in solid form. It is known to the expert in this connection that fine-particle solids, i.e. powder-like solids, which normally also contain relatively high percentages of dust, can be used for coating particles with particulate solids, so-called “powdering”.
According to EP-A-0 711 827, the use of particles consisting predominantly of citrate, which has a certain solubility in water, also leads as a secondary effect to accelerated disintegration of the tablets. It is assumed that the dissolution of the citrate locally increases the ion strength over a transitional period so that the gelling of surfactants is suppressed and, as a result, the disintegration of the tablet is not impeded. According to this patent application, therefore, citrate is not a disintegrating agent in the accepted sense, but acts as an anti-gelling agent.
The proposed solutions mentioned in the foregoing produce the required result in the production of pharmaceutical tablets. Although, in the field of detergents and cleaning products, they contribute towards an improvement in the disintegration properties of washing- or cleaning-active tablets, the improvement achieved is inadequate in many cases. This applies in particular when the percentage of tacky organic substances in the tablets, for example anionic and/or nonionic surfactants, increases. This is one of the reasons why, hitherto, detergent tablets which satisfy stringent consumer requirements have not been commercially available. However, in the field of dishwashing detergents and detergent additives also, tablets do not have a sufficiently high disintegration rate despite an often satisfactory fracture resistance. Increasing the rate at which dishwasher tablets also disintegrate and dissolve can have advantages, particularly for phases which contain active substances that are supposed to be effective at the beginning of the dishwashing process or at relatively low temperatures.
Accordingly, the problem addressed by the present invention was to provide washing- or cleaning-active shapes which would contain a disintegrating agent with a high adsorption capacity for water that would be capable of increasing the porosity or the capillarity of the tablets and which would not have any of the disadvantages mentioned above. Another problem addressed by the invention was to provide a process for the production of these improved washing- or cleaning-active shapes.